What is a computer virus?
A virus is any code or software that runs on a computer unbeknownst
by the owner and causes damage. It may come in a number of forms such
as, trojans, macros, and worms.

Trojans: a program that appears to be legitimate
but is designed to have negative effects on the computer onto which
the program was loaded.

Macros: a computer virus which is embedded
into a document or application (like MS Word, Excel) and all future
documents are also infected until the macro is removed.

Worms: a malicious program that replicates
itself until it fills all of the available space on a hard drive.

How do you stop a virus?
Step 1) First you need to purchase and install some anti-virus software.
There are numerous anti-virus software companies out there and each
have their own merits. Following is a short list of some of the larger
anti-virus vendors:

Step 2) Next you need to configure the software to protect
your computer. Most "off the shelf" products will configure
"by default" to auto-protect your hard disk and to scan incoming/outgoing
email for viruses.Note: Remember that scanning for viruses in real-time
may cause a significant decrease in system performance.

Step 3) Finally you need to ensure that the software
is updating the virus definition files daily. Definition files are usually
downloaded online from a server at the software manufacturer. All
anti-virus software depends on its' definition files to determine
whether or not a particular piece of software may be infected. As
a file comes into your computer, the anti-virus software will scan it for
known types of viruses, the known types are found in the definition
files. To illustrate this point, we'll look at Norton Anti-Virus